In adhesive dispensing systems, a dispensing apparatus such as a dispensing module is generally fed liquid adhesive material from an adhesive melter or another similar adhesive supply component. The adhesive supply component may include a pressure control valve for regulating the flow and pressure of liquid adhesive delivered to the dispensing module. In these pressure control valves, a biasing member such as a coil spring biases a valve element towards a closed position, while the pressure of the liquid adhesive applies a force to move the valve element away from the closed position. During operation, the valve element continuously attempts to achieve an equilibrium state in which the forces applied on the valve element by the pressurized liquid adhesive and by the biasing member equal one another.
One example of a conventional pressure control valve 10 is shown in FIG. 1. This pressure control valve 10 includes a dry spring 12 (e.g., a spring 12 that is isolated from the liquid adhesive) and a dynamic seal 14. More particularly, the pressure control valve 10 includes a valve housing 16 including a liquid inlet 18, a liquid outlet 20, and a liquid passage 22 extending from the liquid inlet 18 to the liquid outlet 20. A valve member 24 is located within the liquid passage 22 and moves towards and away from a closed position against a valve seat 26 in the valve housing 16. The dynamic seal 14 is positioned around the valve member 24 so as to divide a dry spring chamber 28 containing the spring 12 from the liquid passage 22. The spring 12 extends between the valve member 24 and an adjustable stop member 30 secured within the valve housing 16.
As pressurized adhesive from an adhesive supply 31 is pumped through a conduit 32 by a pump 33, at least a portion of the adhesive is bled from the conduit 32 downstream of the pump 33 and upstream of a dispensing module 34 fed by the conduit 32. This bleed flow of adhesive enters the liquid inlet 18 such that the adhesive forces the valve member 24 away from the valve seat 26 against the bias of the spring 12 to enable flow of the adhesive out of the liquid outlet 20 back to an inlet of the pump 33 for further recirculation through the conduit 32. As a result, the pressure control valve 10 regulates the pressure of adhesive delivered to the dispensing module 34 by varying the amount of flow through the pressure control valve 10 as a function of the pressure in the conduit 32. The dynamic seal 14 moves with the valve member 24 and frictionally slides along the valve housing 16. When using highly reactive adhesive materials such as polyurethane reactive (PUR) adhesives, cured bits of the liquid adhesive collect against the dynamic seal 14 and contribute to more rapid wearing of the dynamic seal 14. As a result, the dynamic seal 14 requires more frequent replacement to keep liquid adhesive from contacting the spring 12.
Another example of a conventional pressure control valve 40 is shown in FIG. 2 with the same reference numbers on similar elements from FIG. 1. Similar to the pressure control valve 10 of FIG. 1, this pressure control valve 40 includes a valve housing 42 with a liquid inlet 18 connected to a conduit 32 downstream of a pump 33 and upstream from a dispensing module 34, a liquid outlet 20 leading to an inlet of the pump 33, and a liquid passage 22. However, the pressure control valve 40 of FIG. 2 includes a flooded spring 44 located within the liquid passage 22 for biasing a valve member 46 against a valve seat 26 formed in the valve housing 42. The flooded spring 44 partially surrounds a dead flow area 48 in which minimal flowing movement of the liquid adhesive occurs. Thus, when using highly reactive adhesive materials such as polyurethane reactive (PUR) adhesives, cured bits of the liquid adhesive collect in the dead flow area 48 and slowly cause more sluggish operation of the spring 44. Although this pressure control valve 40 only requires static seals, the flooded spring 44 still requires regular disassembly and cleaning to keep the pressure control valve 40 fully functional.
Consequently, it would be desirable to address these and other concerns associated with conventional pressure control valves.